There are basically 3 types of 401(k)s and an automatic 401(k) feature that may be applied to any of these.

Traditional 401(k)
With a traditional 401(k) plan the employer decides whether or not the company will contribute to the plan and may contribute a percentage of each employee’s compensation to the employee’s account (called a nonelective contribution), or may match the amount employees decide to contribute (within the limits of current law) or may do both. The employer may also have the flexibility of changing the amount of nonelective contributions each year, according to business conditions.
If the employer does contribute to the plan a vesting schedule may be applied for employer contributions.
These plans are subject to annual nondiscrimination testing to ensure that the amount of contributions made on behalf of rank-and-file employees is proportional to contributions made on behalf of owners and managers.

Safe Harbor 401(k)

Under a safe harbor plan, the employer must match each eligible employee’s contribution, dollar-for-dollar, up to 3 percent of the employee’s compensation, and 50 cents on the dollar for the employee’s contribution that exceeds 3 percent, but not 5 percent, of the employee’s compensation or may make a nonelective contribution equal to 3 percent of compensation to each eligible employee’s account.
All employer contributions are 100% vested and the plans are not subject to annual nondiscrimination testing.

SIMPLE 401(k)

Employer contributions to a SIMPLE 401(k) plan are limited to either a dollar-for-dollar matching contribution, up to 3 percent of pay; or a nonelective contribution of 2 percent of pay for each eligible employee.
No other employer contributions can be made to a SIMPLE 401(k) plan, and employees cannot participate in any other retirement plan of the employer. All employer contributions are 100% vested and the plans are not subject to annual nondiscrimination testing.

For a plan to qualify as an Automatic 401(k) the following conditions must be true.

Initial automatic employee contribution must be at least 3 percent of compensation. If initial employee contributions are less than 6 percent they must be set to automatically increase so that, by the fifth year, employee contribution is at least 6 percent of compensation.

Employee contributions are limited to $16,500 for 2009 and 2010 with an additional catch up contributions allowed of $5,500 for participants 50 and over.

Employer contributions must be at least a matching contribution, up to 1 percent of pay and a 50 percent match for all salary deferrals above 1 percent but no more than 6 percent of compensation; or a nonelective contribution of 3 percent of pay to all participants.

In part 4 of our series we will examine Roth plans, Profit Sharing Plans and the New Comparability Profit Sharing Plan.